RBU
rbu = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RBU);
iowrite32(FBE | TUNF | CNTOVF | RBU | TI | RI, ioaddr + ISR);
if (intr_status & (RI | RBU)) {
np->imrvalue = TUNF | CNTOVF | RBU | TI | RI;
iowrite32(FBE | TUNF | CNTOVF | RBU | TI | RI, ioaddr + ISR);